Method and apparatus for drying material



I950 o. A. WRIGHT 2,520,871

METHOD AND APPARATUS FDR DRYING MATERIAL Filed Aug. 2, 194a i 4Sheets-Sheet 1 O//ver A Wr/gh 1 IN VEN TOR.

Aug. 29, 1950 o. A. WRIGHT 1 us'mon AND APPARATUS FOR DRYING MATERIALFiled Aug. 2, 1948 4 Sheets-Sheet 2 0//ver A. Wr/y/n INVE 'NTOR.

ATTORNE YJ 4 Sheets-Sheet. 3

O. A. WRIGHT METHOD AND APPARATUS FOR DRYING MATERIAL Aug. 29, 1950Filed Aug. 2, 194a O/H/er A. Vl/rkghf INVE TOR.

ATTORNEYJ 1950 o. A. WRIGHT METHOD AND APPARATUS FOR DRYING MATERIAL 4Sheets-Sheet 4 Filed Aug. 2', 1948 Mm N @N M m U N 1 A A f m I h w 0 V.B

Patented Aug. 29, 1950 METHOD AND APPARATUS FOR DRYING MATERIAL OliverA. Wright, Houston, Tex., assignor to Wright & Shipley Corporation,Houston, Tex.,

a corporation of Texas Application August 2, 1948, Serial No. 42,118

14 Claims.

This invention relates to improvements in method and apparatus fordrying material and refers more particularly to drying materials whereit is necessary to maintain the temperature of the entire pack ofmaterial to be ,dried below predetermined maximum temperatures whichdeleteriously affect the material.

It has heretofore been proposed to dry certain grains such as rice,maize, flax, oats and the like in drying apparatus wherein the materialto be dried is supported between two opposed perforate walls. A heatedgas, usually air, is passed through the drying chamber in such manner asto alternately enter the chamber through one of the perforate walls andthen through the other perforate wall. The direction of passage of theheated gas through the drying chamber was changed when the temperatureof the material lying closely adjacent the perforate wall through whichthe gas is entering reaches a predetermined maximum temperature. Thismethod of drying materials has been satisfactory to a considerabledegree but some difficulty has been experienced in that at the end ofthe drying treatment there sometimes is a tendency for the materiallying adjacent both perforate walls to reach and exceed the maximumtemperature.

At the final stage of the drying operation, the moisture content of thematerial being dried is very low and the cooling effect of evaporationof the moisture content of the material treated is not especially great.Therefore, the flow of gas in any one direction continues for a verylimited or short period of time. The material on the downstream side ofthe pack of material being dried does not always have sufficient time tocool appreciably during this short time interval. In order to correctthis it was then proposed to discontinue the passing of the gas throughthe pack of material to be dried when this condition was encountered.However, this did not work entirely satisfactorily because when the gasflow through the apparatus discontinued the pack of material being driedwas very slow to cool.

An object of this invention is to provide a method and apparatus fordrying material whereby the temperature of the material to be dried willnever exceed a predetermined maximum temperature to which the materialtreated may safely be heated. 1

Another object is to provide, in a method and apparatus for dryingmaterial supported between two opposed perforate walls wherein gas isfirst passed through the chamber entering first one perforate wall andcontinuing in this direction until the material lying closely adjacentsaid perforate wall approaches the predetermined maximum temperature towhich the material may be safely heated and then the direction of flowis changed so that the heated gas enters the chamber through the otherperforate wall and this is alternately continued, for passing arelatively cool gas through the pack of material to be dried when thematerial lying adjacent both perforate walls approaches the maximumtemperature.

A further object is to provide a method and apparatus for dryingmaterial supported in a drying chamber between two opposed perforatewalls wherein a relatively cool gas is passed through the pack ofmaterial to be dried when the temperature of the material adjacent bothperforate walls approaches the maximum temperature to which the materialshould be heated and wherein this is accomplished automatically.

Still another object of this invention is to provide control apparatusadapted to selectively pressurize two of three stations and topressurize the third station when the first two stations aresimultaneously pressurized.

Other and further objects of this invention will appear from thefollowing description of a preferred embodiment of the invention.

In the accompanying drawings which form a part of the instantspecification, are to be read in conjunction therewith, and wherein likereference numerals are employed to designate like parts of the variousviews:

Fig. 1 is a schematic sectional plan view of apparatus embodying thisinvention;

Fig. 2 is a side elevational view of the drying housing shown in Fig- 1with parts broken away for purposes of illustration;

Fig. 3 is' a cross-sectional view of the apparatus of.Fig. 2;

Fig. 4 is a fragmentary cross-setional view, on an enlarged scale,similar'to Fig. 3 and showing construction details;

Fig. 5 is a schematic view illustrating the con-. trol mechanism foractuating the means for directing the flow of drying medium in theapparatus of Fig. 1;

Fig. 6 is a detail upon an enlarged scale of the mechanism for actuatingthe control valve shown substantially at the center of Fig. 5;

Fig. 7 is a view upon an enlarged scale illustrating the control forenergizing the actuating means of Fig. 6 and also the actuating meansshown in the right hand portion of Fig. 1 controlling the heating means;

. 3 v a Fig. 8 is a view taken along the line 8-8 in Fig. '7 in thedirection of the arrows; and

Fig. 9 is a modified apparatus for actuating the valve means shown inFig. '7.

. Before describing the drawings in detail it is believed best to pointout that in drying certain materials of the character of grain and thelike it is desirable to pass a heated gas through the material andpreferably the gas should be heated greatly in excess of thetemperatures to which the material treated may be safely heated. Usuallytemperatures in the order of 150 may be employed for this purpose whilemost grains cannot be heated to this high a temperature and still beusable for certain purposes. ,These predetermined maximum temperaturesto which the gain may be safely heated are well known to those skilledin the art and for example rice for table use may be safely heated to105 Fahrenheit,- maize for the production of glucose to 105 Fahrenheit,maize for germination purposes to 125 Fahrenheit, flax to be used inprocessing of oil to 100 Fahrenheit, and oats which are to be used asseed oats to 107 Fahrenheit. The apparatus and method of this inventionare especially adapted for use in drying materials of this character andthe material being dried will never be heated to a temperature to exceedthe predetermined selected temperature to which the material may besafely heated for the purpose for which the material is to be used.

Referring now to the drawings more particu- I larly to Fig. 1, a housinghaving opposite side walls I and 2 is provided for the grain or otherproduct to be dried. These side walls are imthe chamber closely adjacentthe perforate walls I5 and I6 and adapted to be embedded into theperforate except for man holes provided therein and closed by covers 3and 4. These covered man holes provided ready access to the interior ofthe housing when it is necessary to make repairs, adjustments and thelike.

The housing has an upper horizontal wall shown at 5 and mounted uponthis wall is a hopper 6 anchored to the wall by a suitable means such asthe angle iron 1. The hopper is so arranged that its outlet openingregisters with an opening in the up er wall 5 of the housing. A slide 8is provided for the purpose of closing this opening in the wall 5.

The housing has a bottom 9 which also has an Opening of substantiallythe same size as the opening in the u per wall 5. The o enings in thetwo walls are aligned vertically and the opening in the bottom 9 has aremovable slide or closure member ID. F

The housing may be supported upon any suitable platform ll carried onthe cross-beams l2 and the uprightsup orts l3. The platform H has anopening I 4 therein which registers with the opening in bottom 9 of thehousing to permit materialto pass from the housing to the platform.

A pair of vertical perforate walls l5 and I6 extend verticallv withinthe housing throughout the width of the housing dividing the housing.into three separate compartments. These walls l5 and l6 are preferablyhighly perforate and may be fabricated from screen mesh or the like. Ofcourse, the openings through the screen wall should be suflicientlysmall to prevent the material to be dried from passing therethrough andat the same time should provide substantially free passage of air orother drying medium through the inner-compartment of the housing. Thisinner compartment provides a drying chamber with a passagewaytherethrough wherein the perforate 4 walls I! and I8 constitute thetermini for the passageway. The two perforate walls l5 and. I8 areanchored to the upper and lower walls 5 and 9, respectively, by angleirons I1 and I8 or other suitable means.

The interior of this intermediate compartment between the perforatewalls l5-- and i6 communicates upwardly with the hopper 6 and downwardlywith the opening 14 in the bottom of the housing. Thus grain or othermaterial to be dried may be'passed from hopper 6 into the drying chamberand, slide [0, when in place, prevents the material from droppingthrough port or opening l4. 4

The walls l5 and [6 preferably are substantially parallel so the body ofthe product to be dried, which is usually referred to as the pack, is ofuniform thickness throughout. Preferably sumcient of the product to bedried is provided in the hopper so that the compartment between Walls i5and IE will be entirely filled even though there should be someshrinkage of the material within the compartment as the drying proceeds,This is desirable in order that there will never be space at the upperend of the pack through which the drying medium might tend to by-pass.

It is necessary to provide means for determining the temperature of theportion of the grain or the other material being treated lying closelyadjacent the perforate walls l5 and I6. In this embodiment of theinvention a control box shown schematically at l9, which will behereinafter more fully described, is attached at one end of .the heattreating compartment of thehousing and has heat sensitive elements 20projecting into body of material being treated during the dryingoperation.

The two compartments at the sides of the drying compartment or chamberare provided at their opposite ends with means for directing flow of thedrying medium through the grain; This means includes vertically arrangedshutters 2| and 22 at one end of the housing and vertically disposedshutters 24 and 25 at the other end of the housing. A means is providedfor actuating these shutters so that the shutter at one end of a givencompartment will be open while the shutter at the opposite end of thecompartment will be closed. Only one of the shutters 2| and 22 will beopen at one time and only one of the shutters 24 and 25 will be open atone time. Each of these shutters 2|, 22, 24 and 25 are pivoted about acentral vertical shaft and may be opened and closed by mechanism to behereinafter more fully described.

Communicating with the shuttered openings at one end of each of theoutside compartments of the housing is a conduit v2! leading from ablower or compressor 28 in the form of a rotor 29 actuated by a suitablepower means connected to pulley 30, the power means is not shown in thedrawing. Theblower is arranged to force air or other suitable dryingmedium through the conduit 21 and through one or the other of theshuttered openings controlled by shutters 24 and 25 whichever is open.The drying medium will, of course, then be forced through the dryingchamber of the housing and out the shuttered opening at the opposite endof the other compartment.

The drying medium, preferably air intermingled with the products ofcombustion from the heating unit, is drawn in through the intake conduit3|, this conduit having an open end 32 at an enlarged diameter portion.The airpasses through the annular space 33 about the outside of theburner housing 34 carried by lateral support 35 integral with conduit3|. This support 35 also provides a passageway from the exterior of theconduit into the burner housing. Extending into the burner housing areburners 38 supplied with gas or other suitable fuel through a supplypipe 31. It is to be understood that other suitable heating means may beemployed where desirable due to economics or other reasons.

The burner housing 34 is closed at its upstream end to prevent theincoming air from blowing through the burner housing and directlyagainst the flame. Air for supporting combustion enters the burnerhousing through the interiorof support 35 and the downstream end of theburner housing is open so that the products of combustion will flow outthrough the downstream end of the burner housing into conduit 3| wherethese products will intermingle with the air. The humidity of the intakeair may be adjusted by use of a container 38, filled with suitablematerial for adjusting the humidity of the air, disposed across theopening 32. This container has perforate walls and does not undulyrestrict the flow of intake air into the conduit 3|.

In accordance with this invention air may be used as a 'drying mediumeven when its relative humidity at atmospheric condition is in theneighborhood of 80%. This is true because the drying medium may have itstemperature increased to the order of 150 F. or even higher, even thoughthe maximum temperature to which the material to be treated can besafely raised is in the neighborhood of 100 to 110 F. At this elevatedtemperature the relative humidity 01'- the air, even containing theproducts of combustion, will be about 15%. and to provide at one end ofthe tube a seal in the material being dried and the change of directionof flow of the drying medium through the drying chamber when thetemperature of the material residing closely adjacent the perforate wallis or iii through which the drying medium is entering approaches themaximum temperature to which the material may be safely heated, thetemperature of the material in the drying chamber may be maintainedwithin a saferange.

It is desirable to provide a control for the burners 36 dependent uponthe temperature of the drying gases before they enter the pack ofmaterial to be dried. This control may be readily provided by mounting aheat sensitive device 33 in the restricted portion of conduit 3|. Thisdevice is then utilized to control a valve or other like mechanism todetermine the rate of supply of fuel to the burner housing 34. Where gasor oil is utilized as the fuel, it is preferred to use a gas-filled tube39 for the heat-sensitive device and to provide at one end of the tube aseal in the form of a bellows 40. This bellows 40 may then be used inconjunction with any suitable valve to control an actuating medium foroperating the valve 4| disposed in line 31 supplying fuel to the burners38.

Referring to the details of this control, throttle valve 4| is connectedby linkage 42 pivoted at 43 to bellows 44. When bellows 44 is energizedwith fluid under pressure, throttle valve 4| is'held in open position.As the pressure within bellows 44 is reduced, the throttle valve ismoved toward closed position. A means is provided for supplying pressurefluid to bellows 44 at a pressure de- 7 pressure of the fluid suppliedto bellows 44.

Valve 48 comprises an outer housing, substantially cylindrical, having aflexible diaphragm 49 at its left hand end as viewed in Fig. 1. Thehousing has a vent 48a and is connected to conduits 4i and 41.Controlling the vent 48a and the opening to conduit 41 is a. valvemember 50, substantially cylindrical in form with one side 50a cut away.Valve 50 is adapted to slide axially within the housing of the valve andin one position will completely close the opening to conduit 41 and inthe other position will completely close the vent opening 43a. Thelength of valve 50 is such that as the valve is moved from one positionto the other, vent 43a will be partially uncovered as the opening toconduit 41 becomes covered. With this arrangement the bellows 44 may becompletely vented or pressurized with the maximum pressure. Also,intermediate pressures valve 30. A spring I2 urgesbellows 40 towardcollapsed position for it abuts the bellows at one end and nut 53carried by bellows housing '54 at the other end.' When the temperatureof the drying medium increases, the pressure in bellows 40 increases tourge the valve member is toward the position to cover the opening toconduit 41. When the temperature of the drying medium decreases, slideill is moved in a reverse direction and throttle valve 4| is movedtoward open position.

Conduits 45 and 46 are connected to bellows 44 through a valve". Thevalve 55 has a passage 55a. Passage 55a is adapted in one position ofthe valve to communicate between conduits 4i and 40 and in the otherposition to communicate between conduit 43 and vent opening "b. I Thisprovides a means for-completely shutting off throttle valve 4| and it isactuated by a mechanism to be hereinafter more fully described, whereby,when the temperature of the material being dried adjacent walls I! andI8 approaches the maximum temperature to which material may be safelyheated, valve 4| will be automatically closed to shut off the fire atburners 36. A suitable pilot, not shown in the drawings, is supplied forburners l6 and has connection with the source of fuel through branchconduit 31a.

It is preferred to provide a control for actuating the means. fordirecting the flowof drying medium through the pack of material to betreated. This control may be manual but it is very diflicult to provideadequate control by the manual method, and it is preferred to employ amechanism which will automatically operate the means for directing flowof drying medium through the pack of material so that the direction offlow of the'medium is positively changed when the temperature of thematerial residing closely adjacent the perforate wall through which thedrying medium is entering the heat chamber approaches the maximumtemperature that the material may be safely heated to. It is alsodesirable to automatically cut on the heating means for heating thedrying medium when the acaaeva forate walls approaches such maximumtemperature. .While this control may be provided by any suitable means,the control must be very accurate to give the best results and also thecontrol mechanism must be rugged in order to stand up under normalconditions of use.

A pneumatic control system has been devised which gives by farthe bestresults yetobtained andwhich is very rugged in operation. pneumaticsystem is sensitive to within /2 F.

Referring to the details of the preferred embodiment of the control, seeFig. 7, a source of constant fluid pressure, not shown in the drawings,is connected through conduit 56 and intermediate or branch conduits andvalves with three pressure stations which may be referred to as stationone shown at 51, station two shown at 58, and station three shown at 59.The arrangement is adapted to provide pressure fluid selectively atstations one and 'two and when both stations are energized I to supplypressure fluid at station three Conduit 5! is connected through branchcon- 7 tion to vent conduit 6|. .With passage 62b mak- Y ing conduits SIand 6| common, pressure fluid is supplied at station one shown at 51.With con-' duit 6i vented, station one is relieved of pressure.

A means is provided for automatically actuating valve 2 whereby stationone is energized when the temperature of the material being driedadjacent one perforate wall of the dryingchamber approachesapredetermined maximum. This may be accomplished by lodging one of theheat sensitive devices 20, which will be referred to by the mnneral 20',in the drying chamber adjacent wall IC. This heat sensitive device is agas 'fllled sealed tube, the seal being provided by bellows 63. Bellows63 is mounted in a housing 64 and has a connecting rod 85 extendingthrough a central e in nut 86. C011 spring 8 is 1' positioned betweennut 66 and the end of the -bellows and urges the bellows towardscollapsed position. By changing spring 81 or adjusting the axialp'ositionof nut fl the, heat-sensitive device may be adjusted to triggerthe valve at a selected Referring to Fig. 9, there is shown, forpurposes of illustrating the principle involved, a

schematic arrangement oi the actuating linkage between'bellows l3 andvalve 52. The rod may be connected directly with the central valvemember of valve 62 by a suitable station one, shown at 51, is thenenergized and will remain energized until the pressure withinheat-sensitive device 20' falls below the predetermined maximum. Whenthis occurs, the linkage 68 ,will be rocked about pivot 89 past centerby the axial shifting of rod 85' and the centralvalve member will beshiftedwithin housing 62 to a position with passage flbcommunieatingbetween conduit BI and vent 82a. 7

Obviously, the movement of rod 65 due to pressure changes within theheat-sensitive device 20 and bellows 68 is a gradual movement as thepressure increases and decreases due to changes in temperature. Noinstruments are commercially on the market at this time which answer tothe requirements of the mechanism-just described. However, there isavailable commercially a valve which will provide a. branch linepressure which varies-in magnitude as a function ofthe temperature of abody of material contacted by a heat-sensitive device. The valvereferred to is manufactured by' Minneapolis- Honeywell RegulatorCompany. This particular valve has a rather complicated structure andinasmuch as it is conventional equipment, it is not deemed necessary toshow and describe the exact structure and operation ofv this valve inthis application. However, thereis shown at 14 and I4 in Fig. 7 of thedrawings, two schematic valves which-illustrate the principle ofoperation of the Minneapolis-Honeywell valve. ventional equipment isemployed because of its availability and its sensitivity and because itlends itself well to use in conjunction with this invention.

Referring to the embodiment oi the control shown in Fig. '7 whichemploys valve 14 and 14', a bellows ii, separate from the bellows whichprovides the seal for the heatrsensitive-device 20, is employed togetherwith valve means ll for selectively supplying an actuating power to optoa predetermined pressure. I The spring 10 and the adjustable linkage 68provides a means for adjusting the sensitivity of the control of thevalve 62 when the pressure within said bellows ll falls below apredetermined limit, thepassage 62b will make connectionbetween conduitsti and vent 62a. Bellows 'H is connected to a source of constant orregulated fluid pressure through conduits ll, 13a, .60 and ifiand'valveI4 controlling flow throughthese conduits. The valve."

, is disposed between conduits i3, and 13a. Valve linkage 68 pivoted at.The coil spring Ill connected between a suitable support and link 68causes a toggle arrangement so that the valve 60 will be actuated toplace passage 62b in' its two operative positions above described. Theposition of the passage is changed when linkage 68 is moved past centerdue to axial displacement of rod 65. Thus, when the temperature withinheat-sensitive device 20' exceeds a predetermined temperature, thepressure within bellows 63 is great enough to overcome spring 61 andshift rod 65 axially to trip toggle linkage 68 and adjust the positionof passage 62b to that shownin Fig. 9 making conduits I and 6| common.Pressure 14 has a diaphram which'is secured to rod 65. The rod 85 issecured atone end to bellows $3 and at the other end to valve member I6within the housing of valve Id. The valve member '16 is adapted tocontrol the vent 15 and the connectionv betwcenthe. valveheusing'ami'conduit 13a. Valve member 16 is long enough to close boththe vent and the connection with conduit 13a, when in an intermediateposition, and when in extreme positions within the housing providescommunication between the interior'of the housing and either the vent I5or the conduit 13a, dependent upon which extreme position the valvemember is in. I a

When the heat sensitive device 20' is cold, valve member 16 is in araised position with the valve housing vented. As the temperature of thematerial about device 20' raises sufliciently to overcome spring 61,valve member I6 is pushed This condownwardly and closes vent II. Afurther increase in temperature about device 20' will effect furtherlowering of valve member 18, cracking the opening between conduit 18aand the interior of the valve housing. This will permit pressure fromthe constant pressure source to enter the housing and also conduit 18and bellows 1 I. This is a closed system and as the pressure within thehousing builds up, the pressure acting on the underside of the housingdiaphragm will raise the diaphragm to shut off conduit 18a. In operationthe pressure within housing of valve 14 will reach a value for any giventemperature of the material surrounding device 20' such that the valvemember 16 will maintain the vent and the opening to conduit 13a bothclosed. As the temperature about device 20' decreases, valve member 16will rise slightly to permit partial venting of the pressure within thevalve housing and then the valve member will again close the vent. Asthe temperature about device 20 increases, valve member 16 will beforced downwardly to uncover the opening to conduit 13a until thepressure within the valve housing increases sufiiciently so that theforce against the diaphram will move the valve member upwardly to closethe conduit opening.

It is believed obvious that the pressure within conduit 13 and bellowsH, as well as the interior of valve 14 will always be a function of thetemperature to which the heat sensitive device 20' is subjected. Thispressure controls the actuation of valve 62.

In practice, it is recommended that the source of constant pressure befifteen pounds gauge and that the pressure within bellows H which willefiect actuation of valve 82 to place the passage 62b in its Fig. 7position be in the order 01 seven pounds.

One advantage of the use of the control apparatus as detailed in Fig. 7is that the pressure within conduit 13 may be employed to control otheroperations when desirable. Another advantage is that the bellows 1| maybe selected to have the proper degree of extensibility due to pressurevariations within a selected range of low pressures.

In rice drying operations, it is usually desirable to change thedirection of flow of drying medium through the rice pack when thetemperature adjacent the perforate wall through which the drying mediumis entering the drying chamber reaches 105 F. With the flow directionchanged, the temperature of the material on the downstream side of therice pack will fall, and it is desirable that the arrangement of thevalve 14, bellows II, and valve 82 be such that the valve 62 will bevented when the temperature drop is in the order of 1 F.

Station two, shown at 58, is energized or deenergized substantially inthe same manner as station one, shown at 51, but in response to heatsensitive device 20". This station communicates with the source ofconstant pressure through branch line conduit 11 and 18 with a valve 62therebetween. This station is energized and de-energized by the sametype equipment and in a, similar manner to that just described inconnection with station one and in the interest of simplicity, furtherdiscussion of the apparatus and method of operation will be dispensedwith, like parts in the apparatus have been given like numerals with theprime differentiating them from the apparatus controlling station one.

Station three shown at 59 is connected with the main conduit 88downstream from branches 88 and 11 by conduits I9, 88 and 8|. Twothreeway valves 82, designated generally as 88 and 84, respectively areinterposed in this communication line. One or the valves is operated bythe bellows 1|, connected to station one by conduit 82 and operatesvalve 83 by linkage 68. The com nection and operation of this valve isexactly the same as the apparatus and operation thereof of the othervalves 62, and in the interest 0! simplicity the parts are given thesame numbers and a discussion thereof and the operation thereof isdispensed with. However, it is pointed out that with station oneenergized, bellows 'II" is energized to make communication betweenconduits l9 and and with station one vented, conduits l9 and 80 are notcommon, A similar arrangement is provided between conduits 88 and 8| inthe form of valve 84 actuated by a. bellows 'II' to which it isoperativeiy connected by linkage 68. This bellows l|"' has a connectionthrough conduit 85 with station two and is energized upon theenergization of this station and is vented upon venting of this station.

,It is believed apparent that with stations one and two energized,station three will be energized, while if either stations one or two arevented, station three will always be vented. Station three is connectedto the fire control shown in Fig. 1 and heretofore described.

Referring to Fig. 6, station one, indicated by numeral 51, is seen toconnect with a pneumatic actuator mechanism including cylinder 86 withpiston 81 reciprocally mounted therein. The piston is connected by link88 to the actuator valve for manipulating the shutters 2|, 22, 24 and25. This valve 89 is a four-way valve and has another actuatingconnection by means of linkage 90 with an actuator connected to stationtwo indicated by the numeral 58. The conduit 58 supplies pressure to theinterior of housing or cylinder 8| to the left of piston 92, when thestation is energized, to force the piston to the right, as shown in thedrawings. Thus, when stations one or two are actuated, they serve toshift valve 89 whereby a pneumatic pressure is supplied, through anindependent system, to actuating means for the shutters 2 I, 22, 24 and25.

Referring to Fig. 5, a schematic actuating mechanism for the shutters isshown. Valve 89 has a connection 93 with a source of constant pressureand has a vent opening 89a. The valve also has connections 94 and 95.Conduit or connection 94 and conduit or connection 95 are each connectedthrough a series of conduits to the pneumatic actuators for, theshutters 2|, 22, 24 and 25. The pistons within cylinders 96 and 91 areconnected to shutters 22 and 24, respectively, by suitable rods.Pressure is supplied to each of these actuators so as to simultaneouslyswing shutters 22 and 24 to an open position while the pressure issupplied to actuators 98 and 99, connected respectively to shutters 2|and 25, so as to maintain these shutters closed. In other words, whenthe connection 95, as shown in Fig. 2, is made common with connection93, the connection 95 supplies power fluid to the pistons withinactuators 96 and 91 on the side of the pistons to cause the rodsconnected to the shutters to telescope within the piston and to swingshutters 22 and 24 open. At the same time, this connection 95 suppliespower fluid to cylinders 98 and 99 on the side of the pistons therein tocause the rods connected to the shutters to be extended and to closeshutters 2| and 25. At this time the connection 94 is vented, thusventing the spent power fluid from the sides of the pistons oppo-' siteto those energized by the connection 95. when the temperature of thematerial residing adjacent the wall l5. approaches the maximumtemperature to which the material should be heated, the controlmechanism will shift the valve member 89b of valve 89 if the materialadjacent the other perforate wall has suiiiciently cooled, wherebyconduit 94 will be connected with conduit 93 to supply pressure fluid tothe cylinders 95, 51, 98 and 99, to cause shutters 22 and 24 to be swungclosed and shutters 2| and 25 to be swung open. The connection 95 willat the same time be vented permitting exhaust of the expended or spentpower iluid from these cylinders.

Referring now to station three, indicated at 59 in the drawings, andreferring to Fig. 1, it will be seen that the station is connected to abellows I", and that the bellows has a link li connected to rod I02pivoted at I03, and adapted to control the position of the central valvemember of valve 55. Thus, when station three is energized, bellows I00will be extended to cause the central valve member of valve 55 to berotated, making connection between conduit 45 and vent 55b. 'Whenstation three is then de-energized, bellows I00 will collapse and thevalve member will be swung to the position that conduit 45 is madecommon with conduit 46 and valve 4| is then controlled solely inresponse to the temperbe dried, entering through one of the perforatewalls l5 and I6 and departing from the chamber through the other.Inasmuch as the heat sensitive devices 20' and 20" reside closelyadjacent the perforate walls It and I5, respectively, when the materialadjacent the wall through which the drying medium enters reaches orapproaches a predetermined maximum temperature to which the material maybe heated for the purpose to which the material is to be used, thecontrol shown schematically at I! and detailed in Fig.7 causes ashifting of shutters 2|, 22, 24 and 25 so'as to cause the drying mediumto pass through the drying chamber from the opposite direction. If inthis operation the material adjacent both perforate walls falls within alimit closely approaching the maximum temperature at which the materialshould be heated, station three of the control will be energized,causing butterfly valve ll to be completely closed. discontinuing theenergization of the heating means. Cool air is then passed by .fan 29through the pack of material to be treated and will always continue toenter through the same perforate wall through which the heated dryingmedium was passed at the time the butergiaed, station three will bede-energized and butterfly valve ll will be opened in response to thecollapse of bellows Ill.

vDuring the dryin operation, the temperature of the drying medium willbe controlled by the heat sensitive'device 39 disposed'in the restrictedportion of conduit 3| and kept within selected limits.

When the heat treatment or drying operation has been completed, thedried material may be withdrawn from the drying apparatus by removingbottom or slide I0. After removal of the dried material, slide l0 may bereinserted and the heat treatment chamber may then be refilled foranother operation.

From the foregoing, it will be seen that this invention is one welladapted to attain all of the ends and objects hereinabove set forth,together with other advantages which are obvious and which are inherentto the structure.

It willbe understood that certain features and sub-combinations are ofutility and may be employed without reference to other features andsub-combinations. This is contemplated by and is within the scope of theclaims.

As many possible embodiments may be made of the invention withoutdeparting from the scope -thereof, it is to be understood that allmatter herein set forth or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

Having described the invention, what is claimed two opposed perforatewalls providing a drying chamber; means for heating a gaseous dryingmedium and forcing themedium through the chamber to selectively enterthe chamber through either perforate wall and leave the chamber throughthe other perforate wall; two heat sensitive devices within the chamber,with one of said dev'ices'closely adjacent one perforate wall and-theother closely adjacent the other perforate wall, said devices adapted tobe embedded in the material to be dried; and a flow and heat controlsystem for the drying medium including means responsive to the heatsensitive devices for shifting the direction of flow of drying mediumthrough the drying chamber when the temperature of the material beingdried, adjacent the perforatewall throughgvhich the drying medium isentering the chamber, approaches the maximum temperature to which thematerial the temperature of the material being dried' which lies closelyadjacent the perforate walls, and reversing the direction of flow ofheated gas when the temperature of the material adjacent the perforatewall through which the gas is entering the chamber approaches a maximumtemperature to which the material being treated may be safely heated andpassing a relatively cool gas through the drying chamber when thematerial adJacent bo'th perforate walls approaches that maximumtemperature. v

3. The method of claim 2 wherein the material is rice and themaximumtemperature is Fahrenheit.

1. Apparatus for drying material comprising 4. The method of dryingmaterial supported in a chamber having opposed perforate wallscomprising the steps of heating a gas and passing the heated gas throughfirst one perforate wall and out the other and then through the latterperforate wall and out the first, determining the temperature of thematerial being dried which hes closely adjacent to the perforate wallsand reversing the direction of flow of heated gas when the temperatureof the material adjacent the perforate wall through which the gas isentering the chamber approaches the maximum temperature to which thematerial being treated may be safely heated and discontinuing the heaing of the gas and passing the unheated gas through the drying chamberwhen the material adjacent both perforate walls approaches said maximumtemperature.

5. In the method of drying material retained between two opposedperforate walls .wherein a gas is heated and passed through the chamberalternately entering the chamber first through one perforate wall andthen through the other perforate wall, the temperature of the materialclosely adjacent to two walls is continuously measured and the directionof gas flow through the chamber is changed when the temperature of thematerial adjacent the walls in which the gas is entering approaches themaximum temperature to which the material may be safely raised for thepurpose to which the material is to be used, the improvement whichresides in the combination therewith of the steps of discontinuingheating of the gas when the material adjacent to both perforate wallsapproaches said maximum temperature and passing relatively chamber, onedisposed closely adjacent each of the perforate walls, means responsiveto the heat sensitive devices to control the means for directing fiow ofgas through the chamber and to control the means for heating the gas.

9. An apparatus for drying material including a drying chamber definedin part by two opposed perforate walls, means for forcing gas throughthe drying chamber, means for directing the flow of gas so as to enterthe chamber selectively through either perforate wall and pass therefromthrough the other perforate wall, means for heating the gas before itenters the chamber, two

' heat sensitive devices within the chamber, one

cool gas through the material for sufficient time to cool the materialadjacent at least one of the perforate walls substantially below saidmaximum temperature.

8. The method of claim 5 wherein the material to be dried is rice andthemaximum temperature is 105 Fahrenheit.

' 'I. In the method of drying material retained between two opposedperforate walls wherein a gas is heated and passed through the chamberalternately entering the chamber first through one perforate wall andthen through the other perforate wall, the temperature of the materialclosely adjacent the two walls is continuously measured and thedirection of fiow of gas is changed when the temperature of the materialadjacent the walls through which the gas is entering approaches themaximum temperature to which the material may be safely raised for thepurpose to which the material is to be used, the improvement whichresides in the combination therewith of the steps of automaticallydiscontinuing heating of the gas in direct response to said measurementswhen the material adjacent both perforate walls approaches said maximumtemperature, and passing relatively cool gas through the material forsufficient time to cool the material adjacent at least one of theperforate walls substantially below said maximum temperature.

8. An apparatus for drying material including a drying chamber definedin part by two opposed perforate walls, means for forcing gas throughthe drying chamber, means for directing the fiow of gas so as to enterthe chamber selectively through either perforate wall and pass therefromthrough the other perforate wall means for heating the gas before itenters the chamber, two heat sensitive devices within the disposedclosely adjacent each of the perforate walls, pneumatic means responsiveto the heat sensitive devices to control the means for directing fiow ofgas through the chamber and to control the means for heating the gas.

10. An apparatus for drying material including a, drying chamber definedin-part by two opposed perforate walls, means for forcing gas throughthe drying chamber, means for directing the now of gas so as to enterthe chamber selectively I through either perforate wall and passtherefrom through the other perforate wall, means for heating the gasbefore it enters the chamber, heat sensitive devices responsive to thetemperature of the material to be dried and lying closely adjacent eachperforate wall, means responsive to the heat sensitive devices tocontrol the means for directing flow of gas through the chamber and tocontrol a means for heating the gas.

11. An apparatus for drying material including a drying chamber definedin part by two opposed perforate walls, means for forcing gas throughthe drying chamber, means for directing the fiow of gas so as to enterthe chamber selectively through either perforate wall and pass therefromthrough the other perforate wall, means for heating the gas before itenters the chamber, two heat sensitive devices within the chamber, onedisposed closely adjacent each of the perforate walls, means responsiveto the heat sensitive devices to control the means for directing flow ofgas through the chamber and to shut off the means for heating the gaswhen the temperature of the material being dried and lying closelyadjacent the two perforate walls exceeds a. predetermined value.

12. Drying apparatus comprising a drying chamber with a gas fiowpassageway therethrough, shutter means adapted to direct flow of the gasthrough the drying chamber selectively in both directions, actuatormeans for operating the shutter means, adjustable means for heating thegas before it passes into the drying chamber, two heat sensitive devicesone adapted. to be disposed in the material being dried closely adjacentboth termini of the flow passage through the drying chamber, pneumaticmeans responsive to said devices for operating the shutter means toreverse the direction of gas fiow through the drying chamber when thetemperature of the material about the heat sensitive device at theentrance terminal of the passageway is greater than a predeterminedvalue and the temperature at the other terminal of the passageway isless than a said value, said pneumatic means adapted to shut off theheating means when the temperature of the material at both heatingdevices is above said maximum value.

13. A pneumatic control adapted to selectively supply control pressurefluid to three stations 18 comprising a main conduit connectable to asource of pressure fluid, three branch conduits communicating with themain conduit and stations one, two and three, respectively, valve meanscontrolling the branch lines communicating with stations one and twoadapted to selectively and independently connect the first two stationswith the main conduit and to vent the stations, two heat sensitivedevices one corresponding to each of the stations one and two andconnected with the valve means to control same, valve means controllingthe branch conduit to station three, means responsive to pressure atstations one and two to control the latter valve means, the

latter valve means adapted to make communication between station threeand the main conduit only when stations one and two are both pressurizedand to vent station three when either of stations one and two is vented.

14. A control'as in claim 13 wherein means responsive to the heatsensitive devices to control pressure fluid from the main conduit andthis controlled pressure fluid is utilized to actuate the valve means inthe branch conduits leading to stations one and two.

OLIVER A. WRIGHT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

